This invention relates to a valve operating system for an engine and more particularly to an improved system for operating a multiple valve system of an internal combustion engine from a single camshaft.
It has been acknowledged that the performance of an internal combustion engine can be improved through the use of multiple intake and exhaust valves. It is a widely common practice to employ four valves per cylinder in connection with high performance engines. Further performance improvements can, however, be achieved if five valves (three intake and two exhaust) are employed for each combustion chamber of the engine. However, when using more than four valves per cylinder, certain problems arise.
In order to achieve a good combustion chamber configuration i.e. a small surface area and small clearance volume, it is necessary to carefully position the valves. This has been achieved by positioning two of the intake valves to reciprocate about respective parallel axes that lie at an acute angle to a plane containing the cylinder bore axis, these valves being the side intake valves. In addition, a center intake valve is also supported for reciprocation about an axis that lies in a plane that is substantially parallel to the planes of reciprocation of the side intake valves but which is disposed at a lesser acute angle to the plane containing the cylinder bore axis. As a result of this configuration, the tip of the center intake valve has extended a greater distance upwardly from the lower surface of the cylinder head than those of the side intake valves. When all valves are operated by rocker arms from a single overhead camshaft, this means that the height of the engine can be substantially increased. The reason for this is that the rocker arm and its adjusting screw adds considerably to the height of the cylinder head and, accordingly the total height of the engine.
In connection with the placement of the rocker arm and its follower which engages the tip of the valve, it has been the normal practice to position the rocker arm and valve reciprocation axes in such a manner that a line drawn between the point of contact of the follower with the tip of the valve and the rocker arm pivot axis and the axis of reciprocation of the valve is at an acute angle when the valve is closed and is at an obtuse angle when the valve is open and is at a right angle when the valve is halfway between its closed and opened positions. This is done so as to reduce stress and wear between the follower and the tip of the valve. However, this type of relationship gives rise to the added height of the engine, as aforenoted.
If the height of the tip of the center intake valve above the cylinder head sealing surface is reduced, than the angular relationship aforenoted can become disadvantageous and give rise to added stress on the valve actuating components. That is, if the height is reduced, the angular relationship aforedescribed may start out at a right angle and then progress to an obtuse angle thus substantially increasing the wear and stress on the components.
It is, therefore, a principal object of this invention to provide an improved valve actuating system for a multi-valve engine which permits optimum valve placement and reduces stress on the valve actuation and wear on the valve actuating components.
It is a further objection of this invention to provide a valve and operating system for an overhead valve and internal combustion engine that permits a compact engine construction and which reduces wear and stress on the valves.
In addition to the angular relationship aforedescribed, the follower which engages the tip of the valve also rolls across an arc on the tip of the valve as the valve is moved between its closed and opened positions. This is because the rocker arm and follower operate about a pivotal axis while the valve operates about a reciprocatory axis. When the tip of the valves is lowered, then the wear pattern on the tips and caused by contact with the followers can move to an off center relationship thus further aggravating wear.
It is, therefore, a still further object to this invention to provide and improved arrangement for permitting a reduction in the height of a single overhead cam multiple valve engine without creating undo wear patterns on the follower and valve tip.